Basic Principles of Serial Data Transmission
2.5 Data Transmission with the 3964(R) Procedure
Point-to-point connection CP 440 Installation and Parameter Assignment
Manual, 09/2007, A5E00057742-03
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2.5 Data Transmission with the 3964(R) Procedure
Introduction
The 3964(R) procedure controls point-to-point data exchange between the communication
processor and a communication partner. As well as the physical layer (layer 1), the 3964(R)
procedure also incorporates the data-link layer (layer 2).
2.5.1 The Control Characters of the 3964(R) Procedure
Introduction
During data transmission, the 3964(R) procedure adds control characters to the information
data (data-link layer). These control characters allow the communication partner to check
whether the data has arrived complete and without errors.
The Control Characters
The 3964(R) procedure analyzes the following control codes:
● STXStart of Text;
start of character string for transfer
● DLEData Link Escape;
data connection escape
● ETXEnd of Text;
end of character string for transfer
● BCCBlock Check Character (3964R only)
● NAKNegative Acknowledge
Note
If DLE is transmitted as an information string, it is sent twice so that it can be
distinguished from the control code DLE during connection setup and release on the send
line (DLE duplication). The receiver then reverses the DLE duplication.
Priority
With the 3964(R) procedure, one communication partner must be assigned a higher priority
and the other partner a lower priority. If both partners begin connection setup at the same
time, the partner with the lower priority will defer its send request.
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